Plate glass mirrors have long been made by wet chemistry processes involving polluting chemicals. One well known process involves forming, by means of wet chemistry methods, a thin layer of tin oxide upon a glass sheet, providing next a layer of metallic silver to a thickness sufficient to render the layer substantially opaque (and highly reflective when viewed through the glass), overcoating the silver layer with a layer of copper, and overcoating the copper layer with a lead-based paint. When the silver layer is not completely opaque, the copper layer may impart a very slight copper tint to the mirrored surface viewed through the lass. The copper layer serves also as a sacrificial layer inasmuch as it will react with oxygen and other contaminants with which it may come into contact and thus protect the silver layer from becoming sulfided or oxidized. The lead-based paint not only protects the back of the mirror from being physically abraded by scratches or the like, but the lead oxide pigment further contributes to the sacrificial protection afforded the silver layer and copper layer.
The wet chemistry methods employed for making mirrors as described above have many drawbacks, not the least of which is pollution. The wet chemistry methods involve the use of aqueous coating compositions which may contain various highly contaminating substances. Once a coating solution has been largely exhausted, disposal of the solution poses a substantial environmental problem. Further, the paint that is employed, being of necessity lead based to provide corrosion protection to the silver layer, may also lead to toxic results if the paint becomes accidentally ingested or if lead or lead compounds from discarded or rejected mirrors or wasted paint leaches into landfills to contaminate water supplies.